1. Field of the Invention
The present invention relates to an etching mask used for micromachining, a method of making the same, an etching method using the etching mask, a magnetic head device and a method of manufacturing the same, which are used for making writing poles and so on of a composite thin-film magnetic head device having a reading head and a writing head, for example.
2. Description of the Related Art
Demands have been increasing for techniques that achieve finer patterns as a reduction has been sought in size and film thickness of a magnetic head device such as a magnetoresistive (MR) head device used for a hard disk unit and various semiconductor devices. Fabrication of a micropattern includes an etching process. Anisotropic etching is required for achieving high etching accuracy in the etching process. Anisotropic etching has such orientation that a sidewall surface of a complete pattern is orthogonal to the surface of a base layer. An example that requires anisotropic etching is a composite thin-film magnetic head device having an inductive reading head and a magnetoresistive writing head. In order to achieve steady performance of the writing head of the magnetic head device, anisotropic etching is required to be performed orthogonally to the substrate for processing the writing pole (top pole) of the head.
As anisotropic etching, dry etching is preferred compared to wet etching achieved through a complete chemical reaction. Dry etching is to evaporate and remove an object, using reactive gas plasma or ion beams thereof A photoresist is generally used as an etching mask for forming a pattern by dry etching.
One of problems found in such an etching process is that not only the workpiece to be etched but also the mask itself is etched. In the case of dry etching using ion beams, in particular, a photoresist mask is easily deformed since the etching speed of the mask by ion beams is high and the photoresist is sensitive to heat. The photoresist film may be made thick in order to prevent such deformation. However, an increased film thickness makes it difficult to maintain anisotropy of etching, which is not desirable for fine pattern fabrication.
To overcome the foregoing problem, a mask utilizing a metal such as copper (Cu) has been fabricated instead of a heat-sensitive photoresist film.
However, if a metal mask is used, a problem still remains, that is, the top and sidewall surface of the mask are removed together with the workpiece through an ion beam application although the etching speed of the mask is decreased. FIG. 14A to FIG. 14C illustrate such a state. As shown in FIG. 14A, a metal mask 101 is formed on a workpiece 100 and ion beam etching is performed. As shown in FIG. 14B and FIG. 14C, not only the surface of the workpiece 100 but also the top and sidewall surface of the metal mask 101 are removed by ion beams 102. As a result, a sidewall surface 101A of the patterned workpiece 100 is not perpendicular but has a cross section having the shape of a trapezoid whose top width is wider than the bottom width as shown in FIG. 14C. The interface between the sidewall surface 101A and the base layer takes a round shape.
In a composite thin film magnetic head device as mentioned above, in particular, if the cross section of a writing pole formed on a gap layer takes the shape of a trapezoid or the interface between the pole and the gap layer takes a round shape, leakage of magnetic flux results and affects data reading and writing. It is therefore desirable that the top surface of the writing pole layer is horizontal and sidewall surface is perpendicular, that is, the cross section is rectangular.
To achieve such a structure, a method is disclosed in Japanese Patent Application Laid-open Hei 3-252907 (1991) wherein a mask made of a metal (such as a nickel-iron alloy) whose etching speed is nearly similar to that of a workpiece is used. However, it is difficult to maintain sufficient anisotropy in this method, too, since the mask itself is removed through dry etching and part of the removed mask redeposits on the mask, and the mask thickness is required to be substantially thick (3 to 7 xcexcm) and so on.
It is a first object of the invention to provide an etching mask and a method of making the same for precisely performing anisotropic etching through dry etching and forming a pattern on a workpiece, the cross section of the pattern being rectangular in shape.
It is a second object of the invention to provide an etching method for forming a pattern whose cross section is rectangular in shape on a workpiece through dry etching using such an etching mask.
It is a third object of the invention to provide a magnetic head device fabricated through the use of such an etching mask, for suppressing flux leakage in a writing pole and achieving stability of writing, and a method of manufacturing such a magnetic head.
An etching mask of the invention is used for selectively etching a workpiece. The mask is made of a metal and has a cross-sectional shape including a rectangular first region that determines a pattern width of the workpiece and a second region that intercepts an application of etching beams to a sidewall of the first region while etching is performed. To be specific, the etching mask is T-shaped in cross section. To be more specific, the cross section includes a vertical bar an end of which comes to contact with a surface of the workpiece and a lateral bar placed on the other end of the vertical bar whose width is greater than that of the vertical bar. The pattern width of the workpiece is determined by the width of the vertical bar. The lateral bar is not necessarily placed on the other end of the vertical bar but may be anywhere along the vertical bar as long as the lateral bar is closer to the other end of the vertical bar.
According to the etching mask, when dry etching such as ion beam etching is performed, the region of the workpiece not covered with the mask is removed by the application of ion beams and the like. At the same time, the beams are applied to the mask itself. However, the beams are not directly applied to the region of the wall of the vertical bar (the first region) obstructed by the lateral bar (the second region). The beams impinge on the region of the vertical bar other than the region obstructed by the lateral bar, and the metal material scatters. Part of the scattered metal redeposits on the region immediately above the point of application of the beam. The redeposit portion intercepts the application of beams to the wall below the redeposit portion. A change in width of the vertical bar is thereby suppressed.
A first method of the invention is provided for making an etching mask made of a metal and having a T-shaped cross section including a vertical bar and a lateral bar. The method includes the steps of: forming a film for mask formation on a workpiece and forming an opening in the film for mask formation, the opening reaching the workpiece and having a specific width; and forming a metal film in the opening and over a region around the opening to form the etching mask and removing the film for mask formation.
In the first method, the thickness of the film for mask formation may be made equal to the height of the vertical bar of the mask, and the width of the opening may be made equal to the width of the vertical bar. The etching mask whose vertical bar has a width and a height as desired is thereby obtained.
A second method of making an etching mask of the invention includes the steps of: forming a film for mask formation having a specific thickness on a workpiece and performing a first exposure on a region of a specific width in the film by such an exposure amount that reaches the workpiece; after the first exposure, forming a T-shaped exposed region by performing a second exposure on a region having a width greater than that of the region exposed through the first exposure by an exposure amount smaller than that of the first exposure; selectively removing the exposed regions of the film for mask formation to form a T-shaped opening; and forming a metal film in the opening of the film for mask formation to form the etching mask and removing the film for mask formation.
In the second method, the thickness of the film for mask formation may be made equal to the height of the mask, the width of the opening of the film for mask formation formed by the first exposure may be made equal to the width of the vertical bar, and the width of the opening formed by the second exposure may be made equal to the width of the lateral bar. The etching mask having a T-shaped cross section whose vertical bar and the lateral bar both have a desired width is thereby obtained.
A third method of making an etching mask of the invention includes the steps of: forming a first film for mask formation on a workpiece and forming a first opening having a specific width that reaches the workpiece in the first film; forming a metal film in the first opening and removing the first film; forming a second film for mask formation on the metal film and the workpiece and then forming a second opening in the second film, the second opening reaching the metal film and having a width greater than that of the metal film; and forming a metal film in the second opening to form the etching mask that is T-shaped in cross section and then removing the second film.
A fourth method of making an etching mask of the invention includes the steps of: forming a first film for mask formation on a workpiece and forming a first opening having a specific width that reaches the workpiece in the first film; forming a metal film in the first opening, forming a second film for mask formation on the metal film and the first film, and then forming a second opening in the second film, the second opening reaching the metal film and having a width greater than that of the metal film; and forming a metal film in the second opening to form the etching mask that is T-shaped in cross section and then removing the first and second films.
In the third or fourth method, the thickness of the first film may be made equal to the height of the vertical bar of the mask, the width of the first opening may be made equal to the width of the vertical bar, and the width of the second opening may be made equal to the width of the lateral bar. The etching mask having a T-shaped cross section whose vertical bar has a desired height and a desired width and lateral bar has a desired width is thereby obtained.
In the foregoing methods of making an etching mask, the metal film is preferably formed by plating such as electroless plating.
An etching method of the invention includes the steps of: forming an etching mask made of a metal and having a T-shaped cross section on a workpiece, and then performing micromachining of the workpiece by dry etching through the use of the etching mask. A fine pattern having a rectangular cross section is thereby obtained.
A magnetic head device of the invention comprises an inductive writing head including a first writing pole, a second writing pole corresponding to the first writing pole, and a gap layer placed between the first and second writing poles. The second writing pole has a rectangular cross section whose sidewall is substantially orthogonal to a surface of the gap layer. Such a configuration allows the first and second writing poles to perform writing without flux leakage.
Another magnetic head device of the invention comprises an inductive writing head including a first writing pole, a second writing pole corresponding to the first writing pole, and a gap layer placed between the first and second writing poles. At least part of the first writing pole, the gap layer and the second writing pole are equal to one another in width and each have a rectangular cross section whose sidewall is substantially orthogonal to a surface of a base layer. Such a configuration allows the first and second writing poles to perform writing without flux leakage.
Still another magnetic head device of the invention comprises an inductive writing head including a first writing pole, a second writing pole corresponding to the first writing pole, and a gap layer placed between the first and second writing poles. The gap layer and the first writing pole are formed through dry etching using an etching mask made of a magnetic material and having a T-shaped cross section, and the etching mask is the second writing pole. Writing is performed by the first and second writing poles formed with the etching mask.
A method of the invention is provided for manufacturing a magnetic head device comprising an inductive writing head including a first writing pole, a second writing pole corresponding to the first writing pole, and a gap layer placed between the first and second writing poles. The method includes the steps of: stacking a layer to be the first writing pole, the gap layer, and a layer to be the second writing pole in this order and then forming an etching mask made of a metal and having a T-shaped cross section on the layer to be the second writing pole; and selectively removing the layer to be the second writing pole by dry etching using the etching mask to form a rectangular cross section.
Another method of manufacturing a magnetic head device of the invention includes the steps of: stacking a layer to be the first writing pole, the gap layer, and a layer to be the second writing pole in this order and then forming an etching mask made of a metal and having a T-shaped cross section on the layer to be the second writing pole; and selectively removing the layer to be the second writing pole, the gap layer, and a region to the middle in depth of the layer to be the first writing pole in this order by dry etching using the etching mask to form a rectangular cross section.
Still another method of manufacturing a magnetic head device of the invention includes the steps of: stacking a layer to be the first writing pole and the gap layer, and then forming an etching mask made of a magnetic material and having a T-shaped cross section to be the second writing pole on the gap layer; and selectively removing the gap layer and a region to the middle in depth of the layer to be the first writing pole in this order by dry etching using the etching mask to form a rectangular cross section.
In the methods described above, it is preferred that any of the methods of making an etching mask of the invention is applied to the step of forming the etching mask.
Other and further objects, features and advantages of the invention will appear more fully from the following description.